Marine Mammal Entanglement
Large Whale Entanglements
The Marine Debris Threat
Humpback whale entangled in gillnet in lower Chatham Strait.
Marine mammal entanglement, or by-catch, is a global problem that every year results in the death of hundred of thousands of whales, dolphins, porpoises and seals world-wide (Reid et al, 2006). The sources of these entanglements are extensive and diverse. Actively-fished gear, marine debris, constituting lost or abandoned fishing gear, and non-fishery-related gear, and other gear types have been involved in marine animal entanglements. The International Whaling Commission recently listed by-catch as a primary concern. Entanglement is considered one of the primary causes of anthropogenic mortality in humpback and grey whales.
NOAA Fisheries' Alaska Protected Resources Division, working with authorized and trained network partners, attempts to safely free large whales from life-threatening entanglements, and, at the same time, help gather valuable information that may reduce the frequency and impact of entanglement in the future.
Deceased humpback whale in seine net.
Please let us know if you see injured, entangled or dead marine mammals in the water or on the beach. Since 1998, NOAA Fisheries' Alaska Protected Resources Division has received more than 130 confirmed reports of entangled large whales. However, the number of animals entangled is certainly much greater since many entanglements go unreported. Scar analysis done on humpback whales in northern Southeast Alaska indicated that 78% (maximal estimate) of the population have scars indicating that the animal had recently been entangled (Neilson, 2007).
Entangled marine mammals may drown or starve due to being restricted by gear, suffer physical trauma and systemic infections, and/ or be hit by vessels due to an inability to avoid them. For Alaska's smaller marine mammals, like the seals and porpoises, death is typically immediate, and due to drowning. However, large whales, like the humpback whale, can typically pull gear, or parts of it, off the ocean floor, and are generally not in immediate risk of drowning. In addition, the impacts of entanglement may be non-lethal, as in the reduction of reproductive success.
Since the threat of entanglement to large whales is not typically immediate, there is time to cut the animal free. However, cutting free a 45-foot, 40-ton, typically free-swimming animal, is not an easy task, and can be quite dangerous for humans and the animal alike. To do so safely, rescuers use a boat-based procedure that is a modification of an old whaling technique called "kegging". Historically, 'kegging' involved attaching barrels or kegs to whales by harpooning them.
In addition to specially designed tools that help responders get hold of and cut free large entangled whales, NOAA Fisheries uses transmitters and receivers to automatically and remotely track an entangled animal over time. The science, called telemetry, is an important tool for whale rescue.
Telemetry buoy, housing a GPS transmitter, tracks an entangled whale. The buoy is attached to the gear entangling the animal.
The Network uses a pair of transmitters – an Argos/ GPS-based and a VHF radio transmitter. Both transmitters complement each other and are placed together on a telemetry buoy that is specially designed to hold the tag(s) and be attached to the entangling gear trailing behind the animal. Telemetry buoys, like the disentanglement tools, are strategically placed throughout the state with trained personnel.
Nine-day track of an entangled whale in southeast Alaska. Animal successfully freed.
In August 2006, Network members tagged an entangled humpback in lower Stephens Passage in Southeast Alaska. The next day the Network was able to respond, re-locate the animal using the transmitters, and cut all wraps of gear from the animal. Unfortunately, lines remained embedded in wounds and thus remained attached to the animal. Over the next 9 days and at least 215 nautical miles, the animal was tracked as it swam southwest along Frederick Sound, south down Chatham Straits, and out to Coronation Island. However, on the 10th day the animal moved back into the sheltered waters of Chatham Strait and conditions allowed a rescue operation to be mounted in which the animal was entirely freed of all gear.
Network and Authorization
Response to disentanglements is coordinated by NOAA Fisheries' Alaska Region Protected Resources Division, and receives authorization under the agency's National Marine Mammal Health and Stranding Response Program (MMHSRP) permit (#932-1905).
Trained stranding network members assess an entangled whale before attempting to cut it free.
Response and Outcome
Stranding network members with the assistance of the US Coast Guard free an entangled humpback whale.
The Alaska network responding to entangled whales has grown since its inception in 1998, and now comprises over 180 participants who have received different levels of training in order to support disentanglement efforts statewide. The network now has 8 caches of specialized equipment strategically distributed throughout the state. Since 1998, the network has received over 130 large whale entanglement reports and mounted more than 80 on-water responses (some reports could not be responded to due to time-of-day, weather, and/or remoteness). These responses totally or partially freed more than 40 large whales from life threatening entanglements. Fishermen are trying to reduce the rate and impact of large whale entanglement in their gear, and assist in disentanglement efforts when appropriate.
While disentanglement may help save some of these animals, it is not the long-term answer. The value of entanglement response is that it provides information that might help managers, fishermen and other ocean users with the ultimate goal of lowering the risk of entanglement for large whales and other marine animals.
NOTE: These are draft numbers and are subject to change.
How to Report Marine Mammal Strandings and Entanglement
Stranding network members receive training on whale disentanglement. Training, proper equipment and authorization is necessary for a safe response.
How You Can Help
- Please call the NOAA Fisheries' 24/7 Hotline at (877) 925-7773 if you see injured, entangled, or dead marine mammals in the water or on a beach. This will alert authorized responders.
- Assist with assessment - The most important information to collect is the date, location (including latitude and longitude), number of animals, nature of the distress (i.e. description of the entanglement), the species involved and its age class (i.e. small animal vs large), and if mobile, the animal's heading and speed.
- Monitor - If responders are on their way, authorities may ask that you watch the animal from a safe distance (greater than 100 yards and not directly behind). Even large whales become large needles in a very large haystack called the North Pacific Ocean. If possible take photos and video of animal and entanglement from a safe distance.
- Stay in the boat - never get in the water to help a whale.
- Wait for trained, authorized personnel - do not attempt to free a whale on your own. Disentangling a large whale is dangerous. Removing trailing lines and buoys may diminish the chances of freeing the animal of all gear, potentially leaving lethal wraps behind.
Online Reporting Form
(for the general public)
Marine Mammal in Distress Report Phone Numbers
- NMFS statewide 24-hour Stranding Hotline: (877) 925-7773 or (877) 9-AKR-PRD
- Protected Resources Office:
- Juneau: (907) 586-7235
- Anchorage: (907) 271-5006
- Alaska SeaLife Center Stranding Hotline: (888) 774-7325
- Large Whale Entanglement Fact Sheet
- All Tied Up: Taking a Closer Look at Humpback Whale Entanglement in Alaska, 1990-2011 (poster)
- About the Stranding Network